1. Field of the Invention
The invention concerns a tomography apparatus with an annular channel and with at least one ventilation element for drawing off an air current flowing through said annular channel.
2. Description of the Prior Art
Using a tomography apparatus, such as a computed tomography apparatus for example, three-dimensional layered images are created of an area to be examined in a patient for the purposes of diagnosis or therapy. The basic structure of a computed tomography apparatus includes a gantry with a stationary supporting frame in which a rotational frame is mounted such that it can be rotated around an axis. Electronic components of a tomography data acquisition system are disposed on the rotational frame, such that through the rotation of the rotational frame with simultaneous constant forward motion of a patient located on a table along the system axis, projections are recorded from numerous different projection directions at various positions of the area being examined. The projections recorded by means of a spiral shaped sampling of this type are transferred to a computing device and converted to a three-dimensional layered image.
A basic thermal problem for all computed tomography apparatuses is that up to 99% of the electrical energy used in generating X-rays is converted to heat. In order to ensure that the operation of the data acquisition system can ensue without problems, it is necessary to draw away the heat generated by the components disposed on the rotational frame. This can be a particularly large challenge when, for sampling the region being examined, a high level of X-ray radiation is required. In such a case, overheating of the X-ray tube must be avoided. The detector must also be cooled during the operation of the computed tomography apparatus, because with increasing heat the signal/noise ratio of the acquired values becomes worse, which results in a reduction of the image quality of reconstructed layered images.
For this reason, computed tomography apparatuses are equipped with a cooling device for cooling the components located on the rotational frame. In principle, a distinction is made between water cooled systems and air cooled systems. Water cooled systems have the advantage that heat generated within the apparatus can be effectively dissipated without heating the surrounding air. These systems can therefore be operated independently of an existing air conditioning apparatus in the examination room. Water cooled systems, however, are very expensive. A less expensive means for cooling a computed tomography apparatus typically is a cooling device that draws air from the examination room and directs it through the computed tomography apparatus. With this system, the air absorbs a portion of the heat given off by the components. The air current heated in this manner is subsequently channeled out of the space by a ventilation element.
Aside from the actual cooling, the reduction of acoustic emissions caused by the cooling system while operating the computed tomography apparatus is an important aspect in the development of the system. Measures for reducing noise are known is this respect, for example, from DE 10 2005 041 542 A1. Between the rotational frame and the supporting frame, an annular channel is formed. The rotational frame, in the known case, contains openings that are distributed randomly on the rotational frame. When the rotational frame is rotating, these openings pass over the gaps incorporated in the supporting frame in a cyclical manner. In this manner, an exchange of air can be produced by means of a constant fluctuation in pressure, which results in a reduction of acoustic emissions.